To continue and complete several ongoing experiments and to prepare for publication results of other studies completed during the past year. In one way or another all experiments deal with normal differences in behavior of male and female dogs, and the first problem is to identify and quantify such differences. The second objective is to discover the extent, if any, to which such sex differences depend on hormonal conditions normally obtaining during prenatal and immediate postnatal development and differentiation. Normal hormonal status is altered by exposing females to testosterone in utero and by castrating males at birth. Types of sexually-dimorphic behavior investigated include the following: urinary activities including "marking" environmental targets, aggression, dominance, competitiveness, mating reactions, response to sexually-significant stimuli such as odor of estrous females, etc.